GNSS and SAR Technologies for Atmospheric Sensing

Editorial Board (September 2019)
Editor-in-Chief
Yasuo Ogawa, Tokyo Institute of Technology, Japan

Vice Editors-in-Chief
Masato Furuya, Hokkaido University, Japan
Solid Earth Science

Nozomu Nishitani, Nagoya University, Japan
Space Science

Editors
Valerio Acocella
Ryosuke Ando
Kimiyuki Asano
Nanan Balan
Paul Bedrosian
Phil Cummins
Hao Dong
Koji Fukuma
Shin-Chan Han
James Hickey
Thomas Hobiger
Hauke Hussmann
Takeo Ito
Art Jolly
Tomokazu Kobayashi
Attila Komjathy

Alexey Kuvshinov
Juanjo Ledo
Huixin Liu
Yohei Miyake
Mitsuhiro Nakagawa
Junichi Nakajima
Haruhisa Nakamichi
Yasuhito Narita
Takuya Nishimura
Takaaki Noguchi
Masahito Nose
Makiko Ohtake
Keiji Ohtsuki
Kyoko Okino
Duggirala Pallamraju
Severine Rosat

Akinori Saito
Tatsuhiko Saito
David Shelly
Hiroko Sugioka
Benoit Taisne
Sunny TamYoshiyuki Tanaka
Yanbin Wang
Yih-Min Wu
Chuang Xuan
Takuji Yamada
Mare Yamamoto
Tadashi Yamasaki
Tatsuhiro Yokoyama
Kazunori Yoshizawa

Hiroo Kanamori
Jun'ichiro Kawaguchi
Takafumi Matsui
Hitoshi Mizutani

Toshitaka Tsuda
Zhongliang Wu
Kiyoshi Yomogida

Advisory Board
Benjamin Fong Chao
Bernard Chouet
Yoshimori Honkura
Toshihiko Iyemori

Journal Scope
Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
The journal was launched in 1998 and has since published over 3000 articles. All of them are available forfree on SpringerLink:
http://link.springer.com/journal/40623
More information about the journal, its article collections, and the submission process is available on thejournal homepage:
http://earth-planets-space.springeropen.com
Submit your next research article to Earth, Planets and Space via:
https://www.editorialmanager.com/epsp
Yours sincerely,
Prof. Yasuo Ogawa
Editor-in-Chief, Earth, Planets and Space
editor-in-chief@earth-planets-space.org

Earth, Planets and Space
Tsuda et al. Earth, Planets and Space (2018) 70:123
https://doi.org/10.1186/s40623-018-0893-6

Open Access

PREFACESpecial issue “GNSS and SAR Technologies
for Atmospheric Sensing”
Toshitaka Tsuda1,6*, Eugenio Realini2, Yoshinori Shoji3, Akinori Saito4, Masanori Yabuki1 and Masato Furuya5

Abstract
Recent advances in the field of atmospheric and ionospheric sensing by GNSS and SAR technologies were discussed
during two workshops held in February 2016 and October 2016 in Italy, hosted by GEOlab of Politecnico di Milano
under partial support of the JSPS Bilateral Open Partnership Joint Research Projects. Another symposium was held inMarch 2017 at the Research Institute for Sustainable Humanosphere of Kyoto University, to discuss (1) the water vapor
and ionospheric maps retrieval from space-borne and airborne SAR, (2) ionosphere and troposphere monitoring by
the ground-based GNSS network and radio occultation, (3) mesoscale numerical weather prediction models anddata assimilation, and (4) ground-based remote-sensing techniques, such as a wind profiling radar. This special issue
collects high-quality papers that describe the findings reported during these three meetings, not limited to GNSS and
SAR, but also including ground-based atmospheric sensing systems and numerical weather prediction models.
Background and scope of the special issue(a) JSPS Japan–Italy bilateral collaborative program
and related meetings.
In 2011, a study on the detection of local-scale precipitable water vapor (PWV) variations, by means of a hyperdense GPS and QZSS receiver network, was carried out
at the Research Institute for Sustainable Humanosphere(RISH) of Kyoto University. This study was conducted incollaboration with the Meteorological Research Institute(MRI) of the Japan Meteorological Agency (JMA), andwith the participation of Dr. Eugenio Realini, originallyfrom Politecnico di Milano (PoliMi), Italy, during his stay
as a postdoc researcher at RISH.
The hyper-dense network was deployed near Uji, Japan,
and comprised 15 receivers with inter-distances of about
1–2 km, covering an area of about 10 km × 6 km. The
study demonstrated the possibility of detecting PWVvariations within the Uji network area, by exploiting
high-elevation slant delays to increase the horizontal
resolution of the retrieved PWV field (Sato et al. 2013).
The collaborative work on the Uji hyper-dense network
continued in the following years, allowing for simulations

and comparisons between the GNSS-derived and NWPderived PWV (Oigawa et al. 2014, 2015).
Stemming from these activities, a JSPS bilateral collaborative program between RISH of Kyoto University and GEOlab of PoliMi was initiated for the period
2015–2017, to strengthen the collaboration between thetwo research groups. The following sections describe theworkshops and seminar that were held in Italy and Japan
under this program.
GEOlab‑RISH workshop in Milan, Italy

The first GEOlab-RISH Joint Workshop on Observations
and Models for Meteorology was held at the Leonardo
Campus of PoliMi, Italy, from February 22 to 24, 2016.
The workshop was meant as an interdisciplinary meeting for the presentation of research activities in the fieldsof GNSS Meteorology, SAR troposphere analysis, mesoscale NWP models, and data assimilation. More than 30
participants joined the workshop, including representatives of the following organizations: RISH, Kyoto University (JP), MRI-JMA (JP), GEOlab, PoliMi (IT), Geomatics
Research & Development srl (IT), Italian Space Agency/eGEOS (IT), University La Sapienza of Rome (IT), University of Genoa (IT), Gter srl (IT), GFZ (DE), Saphyrion
Sagl (CH), University of L’Aquila/CETEMPS (IT), TU
Delft (NL), TU Wien (AT), IRA-INAF (IT), Datameteo*Correspondence: tsuda@rish.kyoto-u.ac.jp
1
Research Institute for Sustainable Humanosphere (RISH), Kyoto
University, Kyoto, Japan
Full list of author information is available at the end of the article© The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.

1

GNSS and SAR Technologies for Atmospheric Sensing
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Page 2 of 5

from Japan, Italy, Germany, Indonesia, China, Taiwan,
Singapore, and South Korea. A total of 44 oral presentations, including 12 invited talks, were delivered in the following sessions:(IT). Several students from both master’s and doctoral
courses attended as well.
The topics presented at the workshop included:• GNSS meteorology• Hyper-dense GNSS networks for troposphere analysis• Innovative GNSS receiver technology and data processing• Innovative GNSS data processing and analysis• Ionospheric delay estimates and models• SAR troposphere products, analysis, and methods• NWP models• GNSS radio occultation• Ground-based measurements• SAR• GNSS: ionosphere modeling, ionosphere variations,
ionosphere irregularities, new applications, GNSS
meteorology, and GNSS radio occultation• Numerical weather prediction models• Ground-based radio and optical remote-sensing
techniques
The discussions at the end of the workshop covered
future collaborative studies in these fields, as well as aproposal for the publication of a special issue. The workshop included a site visit with a technical tour of the Shigaraki MU (middle and upper atmosphere) Radar, which
is known as the most capable atmospheric radar in theworld and is also one of the largest in Asia. Introduction of various atmospheric remote-sensing instruments,
such as the radio acoustic sounding system (RASS) and
Raman lidar, was covered in the tour of the MU observatory. Furthermore, visits were organized to a traditional
pottery production site in Shigaraki and the Byodoin
Temple in Uji, followed by an authentic Japanese tea ceremony experience.

GEOlab‑RISH seminar in Como, Italy

From October 11 to 13, 2016, a Seminar on applicationof GNSS, SAR, and NWP models was held at Como
Campus of Politecnico di Milano. On this occasion, 18
researchers and scientists from Japan, Italy, Denmark,and Germany gave selected presentations on the following topics:• Review of the state-of-the-science of GNSS meteorology, GNSS-RO, SAR, and NWPs
• Ongoing projects and experiments (including realtime PWV monitoring with a hyper-dense GNSS
network, and assimilation of slant total delay into an
NWP model)• Prospective projects (including SAR and GNSS
experiments in the SYNERGY project, and the project of a hyper-dense GNSS network in Tokyo)(c) Scope of the special issue
This special issue consists of eight papers on the measurement techniques and scientific outcomes of the
behavior of the Earth’s atmosphere and ionosphere, utilizing the accurate positioning data obtained by SAR and
GNSS. In addition, as a novel application of the groundbased remote sensing of the atmosphere, the other paper
discussed development of the radio acoustic sounding
system (RASS) for measuring the atmospheric temperature in the tropical troposphere. A total of nine papers
are published in this special issue.

The end of the seminar saw active discussion between
the groups involved in the bilateral program on future
steps of the collaboration, including the organization of
the second GEOlab-RISH Joint Workshop to be held in
Kyoto, Japan.
(b) RISH symposium and a tour to the Shigaraki MU
observatory

Water vapor and ionospheric maps retrieval
from space‑borne SAR
Satellite-based interferometric synthetic aperture radar(InSAR) has been growing over the past nearly three
decades, as a powerful technique to detect surface deformation signals with unprecedented spatial resolution. In
contrast to GNSS technology, however, its applications toatmospheric science have been rather limited because thehigher radar frequencies, such as C- and X-band, haveoften hampered interferometric coherence, particularly
over vegetated areas. Since the launch of the Advanced
Land Observing Satellite (ALOS) by Japan Aerospace

The 2nd GEOlab-RISH Joint Workshop on GNSS andSAR Technologies for Atmospheric Sensing, as a joint
conference of the 331st Symposium on Sustainable
Humanosphere, was held at the Uji Campus of Kyoto
University in Kyoto, Japan, from March 6 to 9, 2017. The
specific purpose was to discuss the technological development and applications of various atmospheric remotesensing techniques and numerical models, following
the 1st GEOlab-RISH joint Workshop and seminar held
in Italy in 2016. The workshop attracted 54 participants2Earth, Planets and Space
Tsuda et al. Earth, Planets and Space (2018) 70:123

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the Earth’s atmosphere. With the advances in GNSS
technology, new research fields such as local-scale water
vapor variation associated with deep convection, water
vapor monitoring over the ocean, and 3D tomography
are beginning to produce results.
Ferrando et al. (2018) present a procedure, termed
G4 M (GNSS for Meteorology), which produces 2D PWVmaps with high spatiotemporal resolution based on asimplified mathematical model, PWV variations withrespect to a “calm” moment, and heterogeneity index(an indicator of a local severe meteorological event). The
G4M maps were compared with meteorological simulations of a severe weather event that occurred in Genoa(Italy).
Barindelli et al. (2018) processed GNSS and weather
station datasets for two heavy rain events and evaluatedthe relationship between the time variations and theevolution of the rain events. The results showed a signature associated with the passage of the widespread rain
front over each GNSS station. The smaller-scale event ofa few kilometers was not detected by the regional GNSS
network, but strong fluctuations in water vapor weredetected by a low-cost station.
Shoji et al. (2017) conducted experimental observations using shipborne GNSS antennas to assess the GNSSPWV over the ocean, from October 19, 2016, to August
6, 2017. A quality control (QC) procedure based on theamount of ZTD time variation was proposed. After the
QC was applied, the retrieved PWVs agreed with theradiosonde observations with a 1.7-mm RMS difference,a − 0.7 mm bias, and 3.6% rejection rate. The differencesin the GNSS PWV versus radiosonde observations werecompared to the atmospheric delay, the estimated altitude of the GNSS antenna, the vessel’s moving speed, thewind speed, and the wave height.
Taking advantage of the ground-based GNSS-total
electron content (TEC) data derived from the nationwide
dense GNSS network (GEONET) in Japan, Muafiry et al.
(2018) examined 3D ionospheric irregularities during thefive cases of midlatitude Es, using a tomography technique. Muafiry et al. also performed several resolution
tests to assess the accuracy of the results and demonstrated the presence of positive electron density anomalies at the E region height. The morphology and dynamics
turned out to be consistent with those reported by earlier
studies.
Noersomadi (2017) investigated a comparison oftemperature (T) profiles from three retrievals of COSMIC GPS-RO (i.e., atmPrf2010, atmPrf2013, andrishfsi2013) with different height resolution aroundthe tropopause. The mean T profiles are consistent
between atmPrf2010 and atmPrf2013, but rishfsi2013
results are slightly colder (warmer) than two other

Exploration Agency (JAXA) in 2006, and its followon ALOS2 in 2014, both of which carry L-band Phased
Array-type L-band Synthetic Aperture Radar (PALSAR
and PALSAR2); however, a growing number of reports ofcrustal deformation over vegetated areas have been published. InSAR application to meteorology has also been
progressing gradually.
Kinoshita et al. (2017) detected wave-like troposphericpropagation delay signals associated with mountain lee
waves by the ScanSAR-mode InSAR observation by PALSAR2 and examined the reproducibility of the signal bynumerical weather simulations. Although mountain lee
waves have been noticed in a number of previous stripmap-mode InSAR observations, Kinoshita et al. (2017)
reveal a more complete image with the use of ScanSAR
mode and demonstrate the uniqueness and usefulness of
InSAR for meteorological application, such as the ability
to map the detailed water vapor distribution regardless ofcloud cover.
Regarding ionospheric impacts on InSAR phase data,no operational corrections for ionosphere have been performed even in L-band InSAR data processing, because
SAR imaging is based on a single carrier frequency. Thus,
there has been uncertainty about how much dispersive
and nondispersive phases are included in L-band InSAR
images. The actual waveform of a radar pulse is, however,frequency-modulated and has a finite bandwidth aroundthe central carrier frequency. The range split-spectrum
method (SSM) can virtually allow for dual-frequency
SAR imaging like GNSS, by splitting the finite bandwidthof the range spectrum. Furuya et al. (2017) reported a
detection of another midlatitude Es by PALSAR2 InSAR
and applied the SSM to separate dispersive and nondispersive components in the InSAR image. While InSAR
SSM allows separation of the phase anomaly into dispersive and nondispersive components, their results indicatethat small-scale nondispersive signals, with similar spatial scale, remain at the same locations.

Ground‑based GNSS network and radio occultation(RO)
Since the 1990s, GNSS has been widely used and has
become an essential part of the earth observation systems as well as a basic infrastructure for human daily
lives. It provides information on electron density, refractivity, temperature, and water vapor under all-weather
conditions that aid atmospheric study as well as operational weather forecasting. The GNSS remote sensing isroughly classified into two methods. The first method
utilizes signal delay observed by ground-based GNSS
receivers, while the other method employs ray bending
caused when the radio path between a GNSS satellite anda GNSS receiver in the low Earth orbit (LEO) traverses

3GNSS and SAR Technologies for Atmospheric Sensing
Tsuda et al. Earth, Planets and Space (2018) 70:123

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Summary
Monitoring of the atmosphere and ionosphere withvarious remote-sensing techniques, from the groundand from satellites, is becoming increasingly important,
not only for improving our understanding of the fundamental processes, but also for advancing prediction
and mitigation systems for natural hazards. This special
issue is devoted to the recent progress on application ofSAR and GNSS for measurements of the atmosphere.
An outline of the three meetings held through the bilateral collaboration between PoliMI and RISH was also
reported. It is hoped that our joint research activities
will be enhanced in the coming years.

retrievals below (above) the tropopause, respectively.
Comparison of three retrievals and 134 co-locatedradiosondes shows that the mean T difference at thecold point of the tropopause from the radiosondes is0.32, 0.49, and − 0.24 K for atmPrf2010, atmPrf2013,
and rishfsi2013, respectively. Similar comparisons of
the lapse rate of the tropopause are showing negative
bias for all GPS-RO retrievals.
Assimilation of GNSS-PWV data into a mesoscale
weather prediction model has been found to be very
useful in improving accuracy. Oigawa et al. (2018)studied the assimilation of high-resolution PWV data
derived from a hyper-dense GNSS receiver network
around Uji city, Kyoto, Japan, which had a mean interstation distance of about 1.7 km. The observed characteristic length scale of water vapor distribution was
small, i.e., 1.9–3.5 km, when it rained over the GNSS
receiver network. The accuracy of the simulated 1-h
rainfall amount was improved by assimilating thehigh-resolution PWV data with small localization radii
over the rainfall area.

Authors’ contributions
TT, ER, YS, AS, MY, MF served as guest editors for this special issue. TT preparedthis preface with the agreement of the other authors. All authors read andapproved the final manuscript.
Author details
1
Research Institute for Sustainable Humanosphere (RISH), Kyoto University,
Kyoto, Japan. 2 Geomatics Research & Development (GReD) srl, Lomazzo,
Italy. 3 Meteorological Research Institute (MRI), Japan Meteorological Agency(JMA), Tsukuba, Japan. 4 Department of Geophysics, Faculty of Science, Kyoto
University, Kyoto, Japan. 5 Department of Earth and Planetary Sciences,
Hokkaido University, Sapporo, Japan. 6 Research Organization of Informatics
and Systems, Tokyo, Japan.

Ground‑based remote‑sensing techniques
The behavior of mesoscale atmospheric disturbancesin the troposphere was studied by using various
observation techniques, such as radiosonde, weather
radar, wind profiling radar (WPR), lidar, and satellite images. Because local and mesoscale effects are
more dominant than synoptic influences in the tropics, continuous observations with the ground-based
remote-sensing techniques are useful. The equatorial
atmosphere radar (EAR) was constructed in 2001 in
Koto Tabang, West Sumatra under intensive collaboration between Japan and Indonesia (Fukao et al. 2003).
EAR is equipped with an active phased-array antenna
and can measure three components of wind velocity.
In addition to winds, the observation of atmospherictemperature is vital for clarification of meteorological phenomena. The radio acoustic sounding system(RASS) (e.g., Matuura et al. 1986) was developed forcontinuous monitoring of atmospheric temperature
profiles, which is a combination of a high-power soundtransmitter and WPR.
Juaeni et al. (2018) conducted eight campaign observations in 2016 of RASS with EAR to measure thetemperature in the tropical troposphere. The acoustic
source location and acoustic frequency range affected
the RASS echoes. The continuous measurement from
August 29 to September 3, 2016, successfully retrieved
the temperature profiles from RASS from 2 to 6–14 km,
with time and height resolutions of about 10 min and
150 m, respectively.

Acknowledgements
We would like to thank all participants for their contributions to the GEOlabRISH Joint meetings, which were organized by RISH, Kyoto University and
GEOlab, Politecnico di Milano (PoliMi), with the support of JSPS Bilateral Joint
Research Projects/Seminars, and joint conferences of the RISH as the 313th
and 331st Symposiums on Humanosphere Science. We deeply appreciate
Professor Andrea Virgilio Monti-Guarnieri, Prof. Giovanna Venuti, and their colleagues at PoliMI, for organizing the 1st GEOlab-RISH workshop in Milano andseminars at Como. We also express our special thanks to Professor Mamoru
Yamamoto, Mrs. Sachiko Shikara, and five students at RISH for their strong
support of the 2nd GEOlab-RISH workshop, including banquet and technicaltour. The symposium and technical tour at Kyoto were partially funded by a
subsidy from Kyoto Prefecture and Kyoto Convention & Visitors Bureau. The
projects of the dense GNSS network around Kyoto, and the study of the GNSS
radio occultation methods for temperature profiles were supported by JSPS
KAKENHI Grant Number 15H03724, and the Research Institute for Sustainable
Humanosphere, Kyoto University (Mission 5-3).
Competing interests
The authors declare that they have no competing interests.
Ethics approval and consent to participate
Not applicable.

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Received: 16 July 2018 Accepted: 16 July 2018

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5

GNSS and SAR Technologies for Atmospheric Sensing

FULL PAPER

Open Access

Detections and simulations of tropospheric water vapor fluctuations
due to trapped lee waves by ALOS-2/PALSAR-2 ScanSAR
interferometry
Youhei Kinoshita*, Yu Morishita and Yukiko Hirabayashi
Earth, Planets and Space 2017, 69:104 DOI:110.1186/s40623-017-0690-7
Received: 9 May 2017, Accepted: 31 July 2017, Published: 15 August 2017

Abstract
Detailed wave-like spatial patterns of atmospheric propagation delay signals associated with mountain lee waves were detected in Hokkaido andTohoku by synthetic aperture radar (SAR) interferometry (InSAR) with the ScanSAR mode observation data of a Phased Array-type L-band Synthetic
Aperture Radar 2 on board the Advanced Land Observing Satellite 2. Both cases occurred under stable atmosphere conditions. The InSARobserved peak-to-trough line of sight changes in the mountain wave signals was 4 and 5 cm with the horizontal wavelengths of 9 and 15 km in
Hokkaido and Tohoku, respectively. Locations of positive phase maxima in the mountain wave signals coincides with locations of cloud streets
observed by visible satellite imagery, indicating that crests of mountain waves contain relatively much water vapor compared with wave troughs.
Numerical weather simulations with the horizontal grid spacing of 1 km were performed to reproduce InSAR phase variations, and as a result thosesimulations could reasonably reproduce observed wave amplitudes and wavelengths in both cases. On the other hand, numerical simulations
tended to overestimate wave attenuation rates: simulated mountain waves decreased as the wave propagated faster than those of observed
signals. Because the simulated wave attenuation rate is sensitive to physics in theplanetary boundary layer (PBL), we investigated the reproducibility of five PBL
schemes implemented in the WRF model. As a result, all the PBL schemes showed little
attenuation except for the Yonsei University scheme (YSU), while the wavelength in
the YSU was most close to the observation. Our study demonstrated the uniquenessand usefulness of InSAR for meteorological application as the ability to map thedetailed water vapor distribution regardless of cloud cover. In addition, the reasonablereproducibility of the water vapor delay signal due to lee waves by the numerical
weather model encourages researchers who tackle the correction of the troposphericpropagation delay, increasing the accuracy in detecting surface deformations.

Keywords: ALOS-2/PALSAR-2, Synthetic aperture radar (SAR), InSAR, ScanSAR
interferometry, Mountain wave, Propagation delay, Water vapor,
Numerical weather simulation

Graphical abstract*Corresponding author: Youhei Kinoshita, kinoshita_youhei@restec.or.jp

FULL PAPER

Open AccessComparison of three retrievals of COSMIC GPS radio
occultation results in the tropical upper troposphere andlower stratosphere
Noersomadi* and Toshitaka Tsuda
Earth, Planets and Space 2017, 69:125 DOI:10.1186/s40623-017-0710-7
Received: 22 March 2017, Accepted: 28 August 2017, Published: 11 September 2017

Abstract
Combining geometrical optics (GO) and wave optics (WO), the COSMIC data analysis and archive center (CDAAC) retrieved two sets of dry atmospheretemperatures (T) from COSMIC GPS radio occultation (GPS-RO), which are called atmPrf2010 and atmPrf2013. In atmPrf2010, the sewing height between WO andGO varies between 10 and 20 km, but is fixed at 20 km for atmPrf2013. The height resolution of the atmPrf2010 depends on the sewing height, while the T profiles
by atmPrf2013 are smoothed over 500 m. We also derived T by applying WO throughout the troposphere and the stratosphere up to a 30-km altitude, which iscalled rishfsi2013. The three retrievals have different characteristics in the height resolution around the tropopause. Therefore, we aim to examine a possible
discrepancy in the statistical results of the cold-point tropopause (CPT) and the lapse rate tropopause (LRT) among the three datasets, conducting their intercomparisons as well as the comparison between GPS-RO and the simultaneous radiosonde dataset. We investigate the T variations in the upper troposphere andlower stratosphere (UTLS) over the tropics from October 1, 2011, to March 31, 2012, when radiosonde
soundings were conducted as the CINDY-DYNAMO 2011 campaign. The mean T profiles are consistent
between atmPrf2010 and atmPrf2013, but rishfsi2013 results are colder (warmer) than the CDAAC
retrievals below (above) the tropopause. The mean T difference between atmPrf2013 and atmPrf2010
is 0.17 K at the cold-point tropopause (CPT) and −0.38 K at the lapse rate tropopause (LRT). On theother hand, rishfsi2013 shows a colder T at CPT by −0.77 and −0.59 K relative to atmPrf2013 andatmPrf2010, respectively, and the warmer T by 0.60 and 0.20 Kd at LRT. During CINDY-DYNAMO, we
found 134 radiosonde soundings that coincide with GPS-RO within ±3 h and are collocated within
200 km from GPS-RO. The mean T difference at CPT from the radiosondes is 0.32, 0.49 and −0.24 K for
atmPrf2010, atmPrf2013 and rishfsi2013, respectively. Both atmPrf2013 and atmPrf2010 have a positive
bias at CPT, while rishfsi2013 has a negative one. Similar comparisons at LRT are −0.45, −0.69 and−0.41 K, respectively, showing a negative bias for all GPS-RO retrievals. The results show that rishfsi2013
is consistent with the retrievals at CDAAC and the radiosondes. Due to its good height resolution,
rishfsi2013 is useful for studies on mesoscale T perturbations in the UTLS.

Keywords: COSMIC, GPS radio occultation (GPS-RO), Full spectrum inversion (FSI), Upper
troposphere–lower stratosphere (UTLS), Retrieval algorithm

Graphical abstract*Corresponding author: Noersomadi, noersomadi@lapan.go.id
6

Earth, Planets and Space

FULL PAPER

Open AccessComparison of shipborne GNSS-derived precipitable water
vapor with radiosonde in the western North Pacific andin the seas adjacent to Japan
Yoshinori Shoji*, Kazutoshi Sato, Masanori Yabuki and Toshitaka Tsuda
Earth, Planets and Space 2017, 69:153 DOI:10.1186/s40623-017-0740-1
Received: 29 August 2017, Accepted: 25 October 2017, Published: 3 November 2017

Abstract
We installed two global navigation satellite system (GNSS) antennas on a research vessel, the RYOFU MARU of the Japan
Meteorological Agency, and conducted experimental observations to assess the GNSS-derived precipitable water vapor (PWV) from
October 19, 2016, to August 6, 2017. One antenna was set on the mast (MAST), while another antenna was set on the upper deck
(DECK). The GNSS analysis was conducted using the precise point positioning procedure with a real-time GNSS orbit. A quality control(QC) procedure based on the amount of zenith tropospheric delay (ZTD) time variation was proposed. After the QC was applied, theretrieved PWVs were compared to 77 radiosonde observations. The PWVs of MAST agreed with the radiosonde observations with a
1.7 mm root mean square (RMS) difference, a − 0.7-mm bias, and 3.6% rejection rate, while that of DECK showed a 3.2, − 0.8 mm, and15.7%. The larger RMS and higher rejection rate of DECK imply a stronger multi-path effect on the deck. The differences in the GNSSPWV versus radiosonde observations were compared to the atmosphericdelay, the estimated altitude of the GNSS antenna, the vessel’s moving
speed, the wind speed, and the wave height. The atmospheric delay and
GNSS antenna altitude showed moderate correlation with the differences.
The results suggest the kinematic PPP’s potential for practical water vapor
monitoring over oceans worldwide. At the same time, from the growing
negative biases with the PWV value and with estimated antenna altitude, it
could be inferred that the difficulty grows in separating the signal delay
from the vertical coordinate under high-humidity conditions.

Keywords: GNSS meteorology, Precipitable water vapor, Kinematic
precise point positioning, Real-time orbits

Graphical abstract*Corresponding author: Yoshinori Shoji, yshoji@mri-jma.go.jp

FULL PAPER

Open Access

Midlatitude sporadic-E episodes viewed by L-band
split-spectrum InSAR
Masato Furuya*, Takato Suzuki, Jun Maeda and Kosuke Heki
Earth, Planets and Space 2017, 69:175 DOI:10.1186/s40623-017-0764-6
Received: 10 August 2017, Accepted: 18 December 2017, Published: 29 December 2017

Abstract
Sporadic-E (Es) is a layer of ionization that irregularly appears within the E region of the ionosphere and is known to generate
an unusual propagation of very high frequency waves over long distances. The detailed spatial structure of Es remains unclear
due to the limited spatial resolution in the conventional ionosonde observations. We detect midlatitude Es by interferometricsynthetic aperture radar (InSAR), which can clarify the spatial structure of Es with unprecedented resolution. Moreover, we use
the range split-spectrum method (SSM) to separate dispersive and nondispersive components in the InSAR image. While
InSAR SSM largely succeeds in decomposing into dispersive and nondispersive signals, our results indicate that small-scaledispersive signals due to the total electron content anomalies are accompanied by nondispersive signals with similar spatial
scale at the same locations. We also examine the effects of higherorder terms in the refractive index for dispersive media. Both of these
10 km
detected Es episodes indicate that smaller-scale dispersive effects
originate from higher-order effects. We interpret that the smallerscale nondispersive signals could indicate the emergence of nitricoxide (NO) generated by the reactions of metals, Mg and Fe, withnitric oxide ion (NO+) during the Es.
-11.9

0

+11.9

cm in slant-range

Keywords: Ionosphere, Sporadic-E, Total electron content,

Interferometric synthetic aperture radar, Split-spectrum
method, Dispersive media, Higher-order refractive index,
Nondispersive media*Corresponding author: Masato Furuya, furuya@sci.hokudai.ac.jp
7a

H 1.289 GHz(Bw=11.9 MHz)b

L 1.226 GHz(Bw=11.9 MHz)

Graphical abstract

GNSS and SAR Technologies for Atmospheric Sensing

FULL PAPER

Open Access

Retrieval of temperature profiles using radio acoustic sounding
system (RASS) with the equatorial atmosphere radar (EAR)in West Sumatra, Indonesia
Ina Juaeni, Hiraku Tabata, Noersomadi, Halimurrahman, Hiroyuki Hashiguchi and Toshitaka Tsuda*
Earth, Planets and Space 2018, 70:22 DOI:10.1186/s40623-018-0784-x
Received: 4 September 2017, Accepted: 17 January 2018, Published: 7 February 2018

Abstract
The radio acoustic sounding system (RASS) with the equatorial atmosphere radar (EAR) at Koto
Tabang, Indonesia was adapted to test the effects of the acoustic source location and acoustic
frequency range on the continuous measurement of height profiles of temperature in the tropical
troposphere. We installed the acoustic transmitting system by using six high-power horn speakers
and four subwoofers. We developed a three-dimensional ray-tracing method of acoustic waves topredict the shape of acoustic wavefronts, accounting for the effects of the background winds on
acoustic wave propagation. Then, we selected the appropriate antenna beam directions for EAR thatsatisfy the Bragg condition between the radar and acoustic wave propagation vectors. We carriedout eight campaign observations in 2016, testing the performance of EAR–RASS. We found that thelocation and acoustic frequency range affected the RASS echoes. We also tested the compensation
method of the background wind velocity with EAR to obtain the true sound speed. We intensively
analyzed the RASS results from August 29 to September 3, 2016, when radiosondes were launched
12 times from the EAR site. We successfully retrieved the temperature profiles from RASS from 2 to
6–14 km with time and height resolutions of about 10 min and 150 m, respectively. Sometemperature profiles were obtained up to about the tropopause at 17 km, although the observation
period was short. During the RASS campaign, we detected a few interesting events regarding
temperature variations as well as large perturbations in the three components of wind velocity.

Keywords: Virtual temperature profile, EAR, RASS, Three-dimensional ray tracing, Tropical
troposphere, Cloud convection

Fig. 16*Corresponding author: Toshitaka Tsuda, tsuda@rish.kyoto-u.ac.jp

FULL PAPER

Open Access

Detection of water vapor time variations associated withheavy rain in northern Italy by geodetic and low-cost
GNSS receivers
Stefano Barindelli, Eugenio Realini*, Giovanna Venuti, Alessandro Fermi and Andrea Gatti
Earth, Planets and Space 2018, 70:28 DOI:10.1186/s40623-018-0795-7
Received: 31 August 2017, Accepted: 31 January 2018, Published: 12 February 2018

Abstract
GNSS atmospheric water vapor monitoring is not yet routinely performed in Italy, particularly at the regional scale. However, in orderto support the activities of regional environmental protection agencies, there is a widespread need to improve forecasting of heavy
rainfall events. Localized convective rain forecasts are often misplaced in space and/or time, causing inefficiencies in risk mitigation
activities. Water vapor information can be used to improve these forecasts. In collaboration with the environmental protection
agencies of the Lombardy and Piedmont regions in northern Italy, we have collected and processed GNSS and weather station
datasets for two heavy rain events: one which was spatially widespread, and another which was limited to few square kilometers. The
time variations in water vapor derived from a regional GNSS network with inter-station distances on the order of 50 km wereanalyzed, and the relationship between the time variations and the evolution of the rain events was evaluated. Results showed asignature associated with the passage of the widespread rain front over each GNSS station within the area of interest. There was apeak in the precipitable water vapor value when the heavier precipitation area surrounded the station, followed by a steep decrease(5–10 mm in about 1 h) as the rainclouds moved past
the station. The smaller-scale event, a convective
storm a few kilometers in extent, was not detectedby the regional GNSS network, but strong
fluctuations in water vapor were detected by a
low-cost station located near the area of interest.

Keywords: GNSS meteorology, PWV variations,
Intense rainfall

Graphical abstract*Corresponding author: Eugenio Realini, eugenio.realini@g-red.eu
8Earth, Planets and Space

FULL PAPER

Open Access

3D tomography of midlatitude sporadic-E in Japan from
GNSS-TEC data
Ihsan Naufal Muafiry*, Kosuke Heki and Jun Maeda
Earth, Planets and Space 2018, 70:45 DOI:10.1186/s40623-018-0815-7
Received: 16 July 2017, Accepted: 8 March 2018, Published: 19 March 2018

Abstract
We studied ionospheric irregularities caused by midlatitude sporadic-E (Es) in Japan using ionospheric total electron content(TEC) data from a dense GNSS array, GEONET, with a 3D (three-dimensional) tomography technique. Es is a thin layer of
unusually high ionization that appears at altitudes of ~ 100 km. Here, we studied five cases of Es irregularities in 2010 and2012, also reported in previous studies, over the Kanto and Kyushu Districts. We used slant TEC residuals as the input andestimated the number of electron density anomalies of more than 2000 small blocks with dimensions of 20–30 km covering ahorizontal region of 300 × 500 km. We applied a continuity constraint to stabilize the solution and performed several different
resolution tests with synthetic data to assess the accuracy of the results. The tomography results showed that positive electron
density anomalies occurred at the E region height, and themorphology and dynamics were consistent with those reported byearlier studies.

Keywords: 3D tomography, Midlatitude sporadic-E, Global

navigation satellite system, Total electron content

Graphical abstract*Corresponding author: Ihsan Naufal Muafiry, ihsanmuafiry@frontier.hokudai.ac.jp

FULL PAPER

Open Access

2D PWV monitoring of a wide and orographically complex
area with a low dense GNSS network
Ilaria Ferrando*, Bianca Federici and Domenico Sguerso
Earth, Planets and Space 2018, 70:54 DOI:10.1186/s40623-018-0824-6
Received: 24 August 2017, Accepted: 24 March 2018, Published: 3 April 2018

Abstract
This study presents an innovative procedure to monitor the precipitable water vapor (PWV) content of a wide and orographicallycomplex area with low-density networks. The procedure, termed G4M (global navigation satellite system, GNSS, for Meteorology), hasbeen developed in a geographic information system (GIS) environment using the free and open source GRASS GIS software (https://
grass.osgeo.org). The G4M input data are zenith total delay estimates obtained from GNSS permanent stations network adjustment
and pressure (P) and temperature (T) observations using existing infrastructure networks with different geographic distributions inthe study area. In spite of the wide sensor distribution, the procedure produces 2D maps with high spatiotemporal resolution (up to
250 m and 6 min) based on a simplified mathematical model including data interpolation, which was conceived by the authors to
describe the atmosphere’s physics. In addition to PWV maps,
the procedure provides ∆PWV and heterogeneity index maps:
the former represents PWV variations with respect to a “calm”
moment, which are useful for monitoring the PWV evolution;and the latter are promising indicators to localize severe
meteorological events in time and space. This innovative
procedure is compared with meteorological simulations in thispaper; in addition, an application to a severe event that
occurred in Genoa (Italy) is presented.

Keywords: Global navigation satellite system (GNSS), Zenith

total delay (ZTD), Precipitable water vapor (PWV),
Severe meteorological event monitoring,
Meteorological simulation

Graphical abstract*Corresponding author: Ilaria Ferrando, ilaria.ferrando@edu.unige.it
9GNSS and SAR Technologies for Atmospheric Sensing

FULL PAPER

Open Access

Data assimilation experiment of precipitable water vapor
observed by a hyper-dense GNSS receiver network
using a nested NHM-LETKF system
Masanori Oigawa*, Toshitaka Tsuda, Hiromu Seko, Yoshinori Shoji and Eugenio Realini
Earth, Planets and Space 2018, 70:74 DOI:10.1186/s40623-018-0851-3
Received: 3 September 2017, Accepted: 25 April 2018, Published: 4 May 2018

Abstract
We studied the assimilation of high-resolution precipitable water vapor (PWV) data derived from a hyper-dense global navigation
satellite system network around Uji city, Kyoto, Japan, which had a mean inter-station distance of about 1.7 km. We focused on aheavy rainfall event that occurred on August 13–14, 2012, around Uji city. We employed a local ensemble transform Kalman filter as
the data assimilation method. The inhomogeneity of the observed PWV increased on a scale of less than 10 km in advance of theactual rainfall detected by the rain gauge. Zenith wet delay data observed by the Uji network showed that the characteristic lengthscale of water vapor distribution during the rainfall ranged from 1.9 to 3.5 km. It is suggested that the assimilation of PWV data withhigh horizontal resolution (a few km) improves the forecast accuracy. We conducted the assimilation experiment of high-resolution
PWV data, using both small horizontal localization radii and a conventional horizontal localization radius. We repeated the sensitivity
experiment, changing the mean horizontal spacing of the PWV data from 1.7 to 8.0 km. When the horizontal spacing of assimilated
PWV data was decreased from 8.0 to 3.5 km, the accuracy of the simulated hourly rainfall amount worsened in the experiment thatused the conventional localization radius for the assimilation of PWV. In contrast, the accuracy of hourly rainfall amounts improved
when we applied small horizontal localization radii. In theexperiment that used the small horizontal localization
radii, the accuracy of the hourly rainfall amount was mostimproved when the horizontal resolution of theassimilated PWV data was 3.5 km. The optimum spatial
resolution of PWV data was related to the characteristic
length scale of water vapor variability.

Keywords: Precipitable water vapor, Dense GNSS

Graphical abstract

receiver network, Data assimilation*Corresponding author: Masanori Oigawa, masanori.oigawa@gmail.com

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Contents
Special issue “GNSS and SAR Technologies for Atmospheric Sensing”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Toshitaka Tsuda, Eugenio Realini, Yoshinori Shoji, Akinori Saito, Masanori Yabuki and Masato Furuya 1
Detections and simulations of tropospheric water vapor fluctuations due to trapped lee waves by ALOS-2/PALSAR-2
ScanSAR interferometry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Youhei Kinoshita, Yu Morishita and Yukiko Hirabayashi
6Comparison of three retrievals of COSMIC GPS radio occultation results in the tropical upper troposphere and lower
stratosphere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Noersomadi and Toshitaka Tsuda 6Comparison of shipborne GNSS-derived precipitable water vapor with radiosonde in the western North Pacific and in
the seas adjacent to Japan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yoshinori Shoji, Kazutoshi Sato, Masanori Yabuki and Toshitaka Tsuda
7
Midlatitude sporadic-E episodes viewed by L-band split-spectrum InSAR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Masato Furuya, Takato Suzuki, Jun Maeda and Kosuke Heki 7
Retrieval of temperature profiles using radio acoustic sounding system (RASS) with the equatorial atmosphere radar(EAR) in West Sumatra, Indonesia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ina Juaeni, Hiraku Tabata, Noersomadi, Halimurrahman, Hiroyuki Hashiguchi and Toshitaka Tsuda 8
Detection of water vapor time variations associated with heavy rain in northern Italy by geodetic and low-cost GNSS
receivers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Stefano Barindelli, Eugenio Realini, Giovanna Venuti, Alessandro Fermi and Andrea Gatti 8
3D tomography of midlatitude sporadic-E in Japan from GNSS-TEC data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ihsan Naufal Muafiry, Kosuke Heki and Jun Maeda 9
2D PWV monitoring of a wide and orographically complex area with a low dense GNSS network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ilaria Ferrando, Bianca Federici and Domenico Sguerso 9
Data assimilation experiment of precipitable water vapor observed by a hyper-dense GNSS receiver network using anested NHM-LETKF system. . . . . . . . . . . . . . . Masanori Oigawa, Toshitaka Tsuda, Hiromu Seko, Yoshinori Shoji and Eugenio Realini 10

Cover image: Ferrando, I. et al., Earth, Planets and Space 2018, 70:54 DOI:10.1186/s40623-018-0824-6